1. Field of the Invention
The present invention generally relates to a reflective liquid crystal display, and more particularly to a method for forming a reflector of a reflective liquid crystal display capable of improving a viewing angle characteristic while simplifying a forming process.
2. Description of the Related Art
As well known, since a liquid crystal display device (hereinafter referred as LCD) is thin in thickness, light in weight and low in power consumption, it is in the spotlight as a display device for personal office automation equipments, an image display device of a television, and so forth. In particular, a reflective LCD is very useful as a portable display element requiring low power consumption because it does not need backlight, and thus there is increasing demand for the reflective LCD as the market for portable equipment, such as portable telephones, grows wider.
Now, a description will be given for a structure of the reflective LCD with reference to FIG. 1. This reflective LCD roughly consist of a lower plate 10, an upper plate 20 and a liquid crystal layer 30 interposed therebetween.
The lower plate 10 includes a lower substrate 1, a thin film transistor (hereinafter referred as TFT) 6 formed on a portion of an inner side of the lower substrate 1, an insulating film 7 vapor-deposited on the lower substrate 1 and the TFT 6, a pixel electrode 8 formed on the insulating film 7, and a lower aligning film 9 formed on the insulating film 7 and the pixel electrode 8.
The upper plate 20 includes an upper substrate 11, a black matrix 12 formed on a portion of an inner side of the upper substrate 11 corresponding to the portion on which the TFT is formed, a color filter 13 formed on both sides of the black matrix 12, a common electrode 14 formed on the black matrix 12 and the color filter 13, and an upper aligning film 15 formed on the common electrode 14.
In addition, the TFT 6 consists of a gate electrode g, a gate insulating film 3, a semiconductor layer 4a, an ohmic contact layer 4b, an etch stopper 5 and source/drain electrodes s, d.
The insulating film 7 is preferably an organic insulating film and has an uneven surface. The uneven surface is obtained by means of a well-known process such as a lithography process or a holography process. Preferably, each of the lower and upper aligning films 9, 15 is a horizontal aligning film.
It is preferred that the pixel electrode 8 is composed of an aluminum metal film having a superior interface reflection characteristic. Also, the pixel electrode 8 is connected to the drain electrode d of the TFT 6 through a contact hole h formed in the insulating film 7. Further, the pixel electrode 8 has an uneven portion 8a due to the fact that the surface of the lower insulating film 7 is uneven. The uneven portion 8a is provided in order to improve a poor viewing angle characteristic by making an incident light from the upper plate 20 be reflected at a larger angle. In the reflective LCD, the pixel electrode 8 usually serves as a reflector.
The liquid crystal layer 30 includes a plurality of liquid crystal molecules 21, and a plurality of dyeing agents 22 which selectively absorb or block the incident light. The dyeing agent 22 has a property to absorb a light passing its long axis and to transmit a light passing its short axis.
The reflective LCD operates according to a principle as described below.
First, when an electric field is not applied between the pixel electrode and the common electrode, the liquid crystal molecules and the dyeing agents in the liquid crystal layer are aligned under the influence of the horizontal aligning film in a state that their respective long axes are parallel to the substrates. If an incident light is projected from the upper plate in this state, the incident light traveling toward the pixel electrode is absorbed in part by the dyeing agents because it passes through the long axes of the dyeing agents, and the rest of the incident light reaches the pixel electrode. Subsequently, the reached incident light is reflected from the pixel electrode and then travels toward the upper plate. In the course of this travel, the light passes through the long axes of the dyeing agents again and thus the dyeing agents absorbing most of the light, which results in a dark state of an image.
On the contrary, when an electric field is applied between the pixel electrode and the common electrode, the liquid crystal molecules and the dyeing agent are aligned in a state that their respective long axes are parallel to a direction of the electric field. If an incident light is projected from the upper plate in this state, the incident light reaches the pixel electrode without being absorbed by the dyeing agent because it passes through short axes of the dyeing agents. Thus, a white state is obtained.
Although the surface unevenness of the pixel electrode, i.e., the reflector is effective to improve the poor viewing angle characteristic of the reflective LCD, there is a problem that a process of forming the surface unevenness, i.e., a non-leveling process is somewhat complicated.
Further, in such a mode that the surface unevenness is used to reflect the incident light at a larger angle, there is another problem that the quantity of light reflected in a normal direction of image, that is, a main viewing direction of a user (hereinafter referred as main viewing angle direction) is very small because most of the incident light is reflected in a lateral viewing angle direction, so that a transmittance in the main viewing angle direction is very low.
Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an objective of the present invention to provide a method for forming a reflector of a reflective LCD, which enables the reflector to be provided with surface unevenness by a simple process.
Another objective of the present invention is to provide a method for forming a reflector, which makes it possible to improve a transmittance in a main viewing angle direction by providing irregular surface unevenness.
To achieve these objectives, there is provided a method for forming a reflector of a reflective LCD in accordance with one aspect of the present invention, the method comprising the steps of: coating a photoresist film on an insulating substrate; dispersing a plurality of spacers over a surface of the photoresist film; curing the photoresist film; rubbing the spacers-dispersed and cured photoresist film, thereby removing the spacers; and depositing a metal film having a high reflectivity on the photoresist film.
Preferably, the metal film having a high reflectivity is an aluminum film. Also, it is preferred that respective sizes of the spacers are unequal. Further, it is desirable that respective quantities of the spacers dispersed over red, green and blue sub pixels are different from one another.
In accordance with another aspect of the present invention, the step of dispersing the spacers over red, green and blue sub pixels while differentiating respective sizes and dispensing quantities of the spacers comprises: providing a red sub pixel opening mask on the photoresist film-coated insulating substrate and dispersing spacers having a first size and a first quantity over the exposed photoresist film portion of the red sub pixel region; removing the red sub pixel opening mask; providing a green sub pixel-opening mask on the photoresist film-coated insulating substrate and dispersing spacers having a second size and a second quantity over the exposed photoresist film portion of the green sub pixel region; removing the green sub pixel opening mask; providing blue sub pixel opening mask on the photoresist film-coated insulating substrate and dispersing spacers having a third size and a third quantity on the exposed photoresist film portion of the blue sub pixel region; and removing the blue sub pixel opening mask.